An observational study of centrally facilitated pain in individuals with chronic low back pain

Supplemental Digital Content is Available in the Text. Indices of centrally facilitated pain, collected early in rehabilitation pathways, are associated with worse pain severity at follow-up. Appropriate early reduction of pain hypersensitivity might improve such outcomes.

asked to press a button on a device held in their dominant hand as soon as the sensation of pressure became painful, thereby electronically storing the pressure value (kPa) on the computer, and simultaneously triggering an audible signal at which the examiner stopped applying pressure.
The procedure was initially applied for familiarisation purposes on the dominant forearm (training site), then repeated a few minutes later on the forearm of the non-dominant arm (testing site) [6].

Temporal Summation (TS)
The tip of the blunt needle was disinfected between individuals with 2% Chlorhexidine in 70% Alcohol. For familiarisation purposes, punctate stimulation was initially applied on the nondominant forearm. For testing, participants were asked to close their eyes and maintain their relaxed position. The 10cm VAS was anchored at left by `no pain/sharpness,' and right by `worst imaginable pain/sharpness'. During rating of the 10 repeated stimuli, participants were asked to rate the experienced intensity of pain or sharpness with sight of their original rating after the single stimulus. A few minutes gap separated the two TS tests. Testing process was conducted after the participant reported that their skin at the test site felt normal to them.

Conditioned Pain Modulation (CPM)
The 11-point NRS had 0 anchored as "no pain" and 10 "the worst pain imaginable".

Pain distribution
The 24-sites of the topographically coded manikin were right or left chest, shoulder, arm, elbow, forearm, hand, thigh, knee, leg, or foot, and head, neck, abdomen, and spinal axis. The Widespread Pain Index (WPI) classification criteria are based on pain shading over at least 4 of 5 regions (left or right upper limb, left or right lower limb, or axis (neck, upper or lower back)).

Central Mechanisms Trait (CMT)
The eight items have each been found to contribute to a single CMT factor in people with knee pain, with good internal consistency and association with PPT evidence of pain hypersensitivity distal to the affected joint [1]. This suggests a link between such items and centrally facilitated pain. To classify participants according to their pain distribution, we considered that one quarter of individuals are anticipated to demonstrate evidence of centrally facilitated pain in CLBP [7], as in other populations with chronic musculoskeletal pain [4; 5; 8].

Clinical characteristics
In the painDETECT questionnaire, participant responses regarding the course, radiation and quality of their pain contributed to a total score (min. 0, max. 38), with higher scores indicating higher likelihood of neuropathic pain.
In the Hospital Anxiety and Depression Scale (HADS), anxiety and depression subscales each have possible ranges from 0 to 21, with higher scores indicating greater anxiety or depression.
was assessed with the Pain Catastrophization Scale (PCS), catastrophization is measured via answering 13 questions with possible answers ranging from 'not at all' (0 points) to 'all the time' (4 points) and possible total scores from 0 to 52. Higher scores indicate higher levels of catastrophizing.
In the Fatigue Severity Scale (FSS), participants were asked to indicate their agreement with 9 statements, each on an 8-point scale (1-strong disagreement, 7-strong agreement), giving a possible summated score from 7 to 63, with higher values indicating higher levels of fatigue.
In the Roland-Morris Disability Questionnaire (RMDQ), participant agreement with 24 statements regarding their ability to perform certain activities (dressing, housework, walking) or functions (sleep) contributed to a total score (min. 0, max. 24). Higher scores indicate greater disability.
In the Fibromyalgia Severity Scale (FMSS), participant responses regarding pain location on body manikin, symptom severity at 3 questions about tiredness, sleep and forgetfulness on a 4-point scale (0-no problem, 3-severe) and whether they experienced headaches, depression or abdominal pain amongst 37 other symptoms were used to calculate a total score (min: 0, max: 31), with higher scores indicating greater severity of fibromyalgia-like symptoms.

Analysis
Distributions of data and of residuals in regression models were evaluated by Shapiro-Wilk normality testing. Where necessary, data were logarithmically transformed before analysis after or without addition of smallest measured value where appropriate. Differences were assessed with paired or unpaired Wilcoxon signed-rank tests, or independent 2-group Mann-Whitney U Tests. The Effect Size was calculated as the difference between baseline and follow-up measurements divided by baseline SD [3].

Supplementary Figures
Supplementary Figure 1

. Depiction of discrete diagrammatic manikin scoring based on 24 anatomical sites.
Classifications are made based on the number of painful sites the pain is distributed other than the main area of pain (lower back and lumbosacral region).

Supplementary Tables
Supplementary Table 1